The problem of preventing unauthorized use of a telephone, especially for the making of outgoing calls, has been important enough to prior investigators to have engendered a number of solutions. Almost all prior solutions were adapted to the french, or desk-type telephone having a separate handset containing receiver and transmitter connected by a flexible cord to a base unit which contained a dialing mechanism and a handset cradle with depressable cutoff buttons. When the handset was replaced in the cradle, its weight was sufficient to depress the cutoff buttons and thereby deactivate the telephone.
A number of inventions in the prior art, for example, Darling U.S. Pat. No. 3,301,969, Winston U.S. Pat. No. 3,469,041, and Medenbach U.S. Pat. No. 2,864,906 depended on locking the handset to the cradle of the desk telephone to maintain it completely inoperative. This, of course, negates the possibility of using the telephone instrument to receive incoming calls. Benson, in U.S. Pat. No. 2,641,659 and Foote in U.S. Pat. No. 3,598,931 achieved the same result by teaching a locking mechanism which maintained the cutoff buttons depressed without captivating the handset. On the other hand, Bart, in U.S. Pat. No. 3,495,050 teaches a shield covering the entire dialing mechanism of a desk telephone while leaving the handset free for receiving incoming calls. None of these inventions is adaptable to preventing unauthorized use of a Trimline telephone of the type having the dialing mechanism located in the handle member of the handset.